1. Field of the Invention
The present invention relates to an apparatus for transporting fluid ink from an ink reservoir to a printhead, which includes a flexible hose having a wall which is in contact with the ink during the transportation, said wall being made of a material which is impermeable or almost impermeable to water and air. The present invention also relates to a hose suitable for transporting fluid ink and the use of such a hose for transporting fluid ink.
An apparatus of this kind is known from U.S. Pat. No. 6,003,981. From this patent specification it is known to use such an apparatus in a large format inkjet printer. In such a printer, a number of printheads carried on a scanning carriage are provided with aqueous ink, the ink being fed from an equal number of reservoirs by means of a plurality of flexible hoses. By using hoses of sufficient length it is possible to provide ink to the printheads even during the printing operation, during which the printheads are constantly moved with respect to a receiving material being printed. In this way printing need never be interrupted to add ink to the printheads.
From the patent specification it is known that the hoses which are utilized possess a number of properties which make them suitable for the described use. The hoses are impermeable or practically impermeable to water (water vapor in this case) and to air. If they are permeable to water, then the ink will lose some of its water through the wall of the hose so that the ink properties change. The ink becomes more viscous which makes it more difficult to jet and there is also created a risk of clogging of the fine nozzles with which the ink is finally jetted from the printhead. Permeability to air can result in too much air being absorbed (or any gas or mixture of gases whatsoever in the printer environment) by the ink. This can also affect print quality or even result in a breakdown of the printing elements (which often contain fine ink ducts in the printhead). In addition, through the absorption of air from the environment, it is difficult to maintain a negative pressure in the ink supply system, and this is necessary in order to avoid ink leakage at the front of the print head. In addition to being substantially impermeable to water and air, the hoses must be flexible, i.e. their modulus must also be sufficiently small since otherwise excessive forces will be exerted on the scanning carriage. In addition, the sensitivity to kinking is relatively considerable in hoses which are not flexible. Kinking is undesirable because the ink supply which is conveyed through the associated hose experiences too great a resistance. Finally, the hoses are preferably durable so that they can retain all of these desired properties for a long time, typically corresponding to some hundreds of thousands and even millions of passes of the scanning carriage. According to the patent specification, for this purpose hoses are used which are made of polyvinylidene-chloride copolymer (PVDC). Such materials, which typically contain 80% vinylidene chloride monomer and 20% vinyl chloride monomer meet the above requirements. However, when such hoses are used, it has been found that the printheads at the front, i.e. the side from where the ink is jetted, become very soiled with ink after a long and intensive use. Such soiling has a negative influence on the print quality, on the one hand, because the jetting of the ink is influenced by the presence of soiling around the nozzles, and on the other hand, because the ink could drip unwantedly onto the receiving material for printing. It has also been found that when the ink is stationary in the hoses for a long period intensive clotting or thickening of the ink occurs in the hoses despite the fact that the wall of the hose is substantially impermeable to water. Such clotting or thickening results in clogging of the hose and accordingly a breakdown of the corresponding printheads. These effects are particularly present when black ink is used.
The object of the present invention is to provide an apparatus which, even with long and intensive use, does not result in intensive soiling of the front of the printhead and wherein the hoses do not clog, even if the ink is stationary within the hoses for long periods of time. To this end, a hose and a printing apparatus has been developed wherein the hose material is made to be substantially resistant to carbon-containing ink.
It has surprisingly been found that the hose according to the present invention does not result in the soiling of the front of the printhead and that the ink, even if it is stationary within the hose for a long period of time, does not show any propensity for clotting or thickening such that the hose containing this ink would tend to clog. The reason for this is not completely clear, but it would appear that in the known hoses there is at least a partial disintegration, chemical and/or physical, of the hose material which takes place in the presence of carbon particles which are frequently used as the black pigment in the ink. The probable cause of the problems is that the disintegration products or specific components from which the material of the hose is made tend to collect at the front of the printhead where it can be more readily wetted by ink leading to a considerable soiling of the printhead. The clotting or thickening of the ink is possibly the result of a gelling process because, despite the non-evaporation of water through the wall of the hose, a considerable thickening of the ink nevertheless occurs. Possibly one or more disintegration products or other substances originating from the material of the hose act as a gelling agent in the ink. With the use of an apparatus in which the material is resistant to carbon-containing ink, i.e. the material experiences no substantial change when in contact with such an ink for a long period of time, these problems do not occur at least occur less rapidly, under the above circumstances. The skilled man can readily determine whether a material experiences such a substantial change. For example, the mechanical properties and/or the composition of the material, either quantitatively or qualitatively, before and after exposure to ink for a long period of time, for example, for several months up to a year, can be determined. If the properties have do not substantially changed, then it is a material according to the invention and with it an apparatus according to the invention can be obtained. Furthermore, it is immaterial to the present invention whether or not the material is homogeneous, a blend, a composite, or of any consistency.
It is also known from WO 98/31546 to use hoses wherein at least the inner wall is made of polythene or polytetrafluoroethylene (Teflon). Polythene materials are substantially impermeable to water (water vapor in this case) but they have been found to have a relatively highly permeability to air or other gases. Consequently such hoses do not meet the requirements for high-grade use. The hoses made of Teflon are very stiff and hence not flexible. This restricts the possible applications of such hoses. Therefore, they are even further removed from the present invention.
In one embodiment, the material of the hose is an alkylene alkyl-acrylate copolymer, wherein the alkylene moiety is selected from the group consisting of ethylene and propylene and the alkyl-acrylate moiety is selected from the group consisting of methyl, ethyl, propyl and butyl acrylate. It has been found that a material of this kind can be used in a printing apparatus according to the present invention because it has been found to be resistant to carbon-containing inks. Even with very long exposure to such ink, the material exhibits no perceptible change in properties or composition. Also, it has been found that this material can be easily processed to form hoses, for example by extrusion. This is surprising because the high melt flow index (MFI) of such acrylate copolymers would lead one to expect that this material would be difficult to process, if it could be processed at all, in such a process.
In another embodiment, the material is a copolymer of ethylene with the alkyl-acrylate. With a copolymer of this kind it is possible to make a hose which is even more flexible and has less tendency to kinking so that the risk of the hose being closed off is further reduced. Also, this material is relatively cheap.
In another embodiment, the alkyl-acrylate is selected from the group consisting of methyl and ethyl acrylate. Such copolymers are very flexible and pass even less water than the propyl and butyl acrylates. In this way the apparatus according to the present invention can be further improved. In a preferred embodiment, the copolymer is an ethylene methyl acrylate. It has been found that such a copolymer is the most flexible and that the water and air permeability are minimized. The resistance to carbon is also good.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.